Decoding the role of ρ mesonic states for elucidating the e+e−→a2(1320)π data and other reactions

Recently, the BESIII Collaboration observed a ρ-like structure Y(2044) in e+e−→a2(1320)π, suggesting that Y(2044) may be a candidate of vector meson ρ(2D) by comparing resonance parameters. However, the theoretical prediction for the combined branching ratio Γe+e−Ba2(1320)π for the pure ρ(2D) state is about 2 orders of magnitude smaller than the experimental value. To resolve this discrepancy and decipher the nature of Y(2044), this work proposes an S−D mixing scheme to reanalyze the cross section of e+e−→a2(1320)π, and finds that the aforementioned branching ratio discrepancy can be resolved. Our results show that the Y(2044) structure can be reproduced by introducing four theoretically predicted S−D mixing ρ meson states ρ3S−2D′, ρ3S−2D′′, ρ4S−3D′, and ρ4S−3D′′ as intermediate resonances, in which dominant contribution arises from ρ3S−2D′′ and their inference effect is also significant. Furthermore, we reanalyzed five additional isospin vector processes e+e−→ωπ0, e+e−→f1(1285)π+π−, e+e−→π+π−, e+e−→ρη, and e+e−→η′π+π− based on the same S−D mixing framework, and simultaneously reproduced their experimental cross section data. This work provides a unified framework to elucidate all observed ρ-like structures near 2 GeV in the e+e− annihilation processes, and suggests that the S−D mixing effect may be crucial for understanding the mass spectrum and decay behaviors of the higher ρ meson states.